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Eternity II

Eternity II:
the puzzle that beat everyone.

Eternity II looks like a children's jigsaw: 256 square pieces, match the colors. Launched in 2007 with a $2 million prize, it has never been solved: not by people, not by supercomputers. This site lets you feel why, right in your browser.

Start herePlay Eternity II onlineWhat is Eternity II?

A full 16×16 board, every edge matched and the border grey — this is what a solved Eternity II looks like. (It's a randomly generated board, not the official puzzle.)

The Puzzle
256 pieces, 22 motifs, a $2 million prize nobody ever claimed. The full story and anatomy of Eternity II.
Playground
Solve a small one yourself, watch a real solver run at a million steps per second, or design its search path.
Algorithms
Backtracking, binary tricks and exponential walls: how computer scientists actually attack the puzzle, explained from scratch.
Board Viewer
Display and share any board. Fully compatible with e2.bucas.name links, including the famous 467/469/470 record boards.
Research
Papers, community records, solver internals, and an open lab notebook of attempts at the full 480.
For classrooms
Built for Terra Numerica: a hands-on way to discover combinatorial explosion, algorithms and why "simple-looking" can mean "impossibly hard". No prerequisites needed.